The research in this proposal examines the role of the endocrine and nervous systems in the regulation of maternal behavior. Recently, we demonstrated a central site of action for prolactin (PRL) in the induction of maternal behavior in female rats. In a series of studies using a rat model we propose to delineate the role of PRL and critically evaluate the possible contribution of the conceptus through its secretion of placental lactogens to the onset and maintenance of maternal care. The central hypothesis tested is that The Onset and Maintenance of Maternal Care Are Regulated Through Common Prolactinergic (Lactogenic) Mechanisms. The first set of studies will define the minimal dose of PRL needed to stimulate the onset of maternal care when infused into the medial preoptic area and clarify the roles of estradiol and progesterone in PRL's central action. A second series of experiments will determine the neural specificity of PRL's action. Next, we will evaluate the biochemical specificity of lactogenic regulation of maternal behavior. The role of rat placental lactogens (rPLs) in the induction of maternal behavior will be assessed by quantifying lactogen concentrations in cerebrospinal fluid during pregnancy and lactation and then measuring the behavioral effects of grafting rPL-secreting, choriocarcinoma (Rcho-I) cells beneath the renal capsule. the effects of direct central infusions of rPL-I and rPL-II on maternal behavior will then be measured, and the possible central actions of nonlactogenic hormones on maternal behavior evaluated. In order to identify neural PRL receptor sites, monoclonal antibodies to the PRL receptor will be biotin-labeled and possible central sites of lactogenic action localized by immunocytochemistry. The involvement of PRL in ongoing maternal care will then be examined in lactating rats. Finally, the possibility that an "up-regulation" or increased sensitivity of a neural lactogenic system develops during the postpartum period will be evaluated. The results of these studies will increase our understanding of the biochemical and neural regulation of maternal care in mammals and provide a basis for evaluating the effects of endocrine and neurochemical imbalances on mother-young interactions.